This invention relates to an apparatus for separating sheets from a stack, and to a method for separating sheets from a stack.
Such an apparatus and such a method are known from practice and are used in many variants in devices that process sheets of paper, such a photocopiers, printers and inserter systems. In such known devices, the separation is carried out by sliding an outer sheet or an outer set of sheets off the stack and arresting, through separation means, any further sheets that move along with the outer sheet or the set of outer sheets, in order to take only one sheet or one set of sheets from the stack. A problem with such methods is that friction between sheets to be separated must be overcome by friction forces that are exerted on those sheets by transport and separation surfaces. This imposes stringent requirements on the friction coefficient between the transport and separation surfaces on the one hand and the sheets on the other, in particular if it should be possible to process a relatively large variety of kinds of paper or if unfavorable conditions, such as a high relative degree of humidity or a low temperature, prevail. Especially in so-called bottom feed separation systems, in addition, a great frictional force occurs between the sheets to be separated in that the rest of the stack bearing on the bottom sheet or the bottom set of sheets exerts a great normal force on the sheets to be separated. According as the stack above the sheets to be separated has a greater height, this problem occurs to a greater extent.
In order that, at a given normal force, more friction can be generated between the transport and separation surfaces on the one hand and the sheets on the other than the mutual friction between sheets to be separated, relatively soft kinds of rubber are utilized for the transport and separation surfaces. However, such kinds of rubber have little wear-resistance and exhibit a greatly decreasing roughness upon ageing. Also, fouling of the transport and separation surfaces and the action thereon of inks provided on processed papers have an adverse effect on the roughness of the transport and separation surfaces. Generally, with such separation systems the degree of reliability desired by the users is not achieved in practice then.
In addition, for large-scale applicationsxe2x80x94such as the processing of sheets in printing officesxe2x80x94it is known to separate sheets by taking them off a stack using suction cups communicating with a partial vacuum. Generally, such systems have the inherent drawback that they are complicated in construction and occupy much space. Further, for separating sets of sheets, special measures have to be taken to ensure that the mutual connection between the sheets of a set remains intact during separation and feeding of the sets. Another drawback of such systems is that they are not suitable for applications where the side of the stack where the sheets are taken off abuts against an abutment structure. This is the case, for instance, with so-called bottom feed systems.
The object of the invention is to enable the separation of sheets or sets of sheets from a stack with a greater reliability than has been attainable heretofore with the known separation system working on the basis of friction, using equipment that is simpler and more compact than that in which sheets are taken off a stack using suction cups.
This object is achieved in accordance with the invention by providing an apparatus for separating an outer sheet or an outer set of sheets from a stack, comprising a holder with at least one guide for guiding a stack of sheets and with an abutment structure which defines an abutment plane for keeping a stack of sheets in the holder in a position with an outer sheet positioned against the abutment plane, wherein the abutment structure is provided with a slit for allowing a sheet or a set of sheets to pass therethrough, which slit is movable relative to the at least one guide along the abutment plane along a path with a directional component transverse to the slit for at least partly peeling an outer sheet or an outer set of sheets abutting against the abutment structure from a stack of sheets in the holder. The invention further provides a method for separating an outer sheet or an outer set of sheets from a stack, which sheet or set of sheets abuts against an abutment plane defined by an abutment structure, comprising bringing opposite to or into a slit in the abutment structure a corner or edge portion of the outer sheet or of the outer set of sheets and displacing the slit along the abutment plane along a path with a directional component transverse to the longitudinal direction of the slit, whereby at least a portion of the outer sheet or the outer set of sheets passes through the slit.
Owing to the abutment structure being provided with a slit movable relative to the stack in the holder along the abutment plane, with a directional component transverse to the slit, an outer sheet or an outer set of sheets abutting against the abutment structure and of which a corner or edge portion is located opposite to or in the slit can be peeled off the stack without that sheet or that set of sheets needing to slid relative to the stack while being peeled off the stack. During the displacement of the slit at least a portion of the outer sheet or the outer set of sheets passes through the slit, basically in the manner of a slice of cheese passing through a cheese slicer while being sliced off. For that matter, the stack can abut against the abutment plane from above, from the side as well as from below.
Because the sheets, while being separated from the rest of the stack, do not slide relative to other sheets of the stack, problems resulting from friction between the sheets to be separated are avoided.
The displacement of the slit in the abutment structure can be realized in a simple manner and displacements of the sheets being separated are simply controlled, during the passage through the slit, by the slit which at the same time forms a guide for the sheets. Thus the apparatus and the method according to the invention can be realized in a simple manner and in a limited space.
Further objects, advantages and embodiments of the invention appear from the claims and the following description on the basis of exemplary embodiments with reference to the drawings.